JPH024402B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method of joining narrow plywood or short plywood to make wide or long plywood, and specifically improves the finger shape and joining method of the conventional finger joint method. The object of the present invention is to provide a joining method suitable for joining thin plywood boards with a thickness of about 15 mm or less. Conventionally, the scarf joint method as shown in Fig. 1 has been a common method for joining plywood, and most of the plywood used has a thickness of about 2.5 to 4 mm. However, in the scarf joint method, in order for the joint part to have the same strength as the plywood material, it is necessary to increase the length b of the joint part by 8 to 12 times the thickness a of plywood 1 and 2. The overlapping area is large and there is a lot of loss. In addition, when joining, the plywood must be pressed until the adhesive used on the joint surface is completely cured, which reduces the workability of joining and makes it easy for the plywood to shift relative to each other during pressing. The bonding surface was difficult to obtain. On the other hand, as a method for joining relatively thick wood such as laminated wood and sawn boards, the finger joint method as shown in Fig. 2 is common. Since the finger joint method is a method of joining a pair of pieces of wood 3 and 4 processed into a finger shape that completely fit each other, the overlapping area of the pieces of wood 3 and 4 is adjusted by adjusting the pitch and length of the fingers. This allows the ratio to the thickness of the wood to be adjusted, reducing loss due to overlapping of wood, which was a drawback of scarf joints. Also, regarding the workability of joining wood,
Since there is no misalignment between the pieces of wood simply by fitting the fingers together, there is no need to press the pieces of wood together until the adhesive has hardened, and the drawbacks of the scarf joint described above are greatly improved. Therefore, if the finger joint method can be used for plywood and thin plates with a thickness of about 15 mm or less, the loss of plate material will be reduced and the joining work efficiency will be greatly improved.
In the case of plywood or thin plates, there are limits to the pitch and length of the fingers that can be processed, making it impossible to obtain the desired strength and smoothness of the joint surface. That is,
Regarding the bending strength of the finger joint, even if the overlapping area of the joints is increased, stress tends to concentrate on the butt joints 5 on the front and back surfaces of the plate material. In particular, when plywood is used, as shown in Fig. 3, the fiber directions of the veneers constituting plywood 1 and 2 are alternately orthogonal, so the veneer 6 whose bonding direction and the fiber direction of the veneers are orthogonal The strength of the part hardly contributes to the bending strength of the joint. Therefore, if a butt joint 9 is applied that cuts the front veneer 7 or the back veneer 8 of plywood, the bending strength of the joint will be reduced to about 30% of that of the plywood material. Also, when fitting the fingers together, if the thickness of the wood is thin or if it is plywood, the veneer may split at the 6 parts where the joining direction and the fiber direction of the veneer are perpendicular, or the joining part may swell, resulting in a smooth joining surface. Hard to get. Therefore, as a result of studying the finger joint method using plywood as a plate material, the present inventor first found a way to improve and stabilize the strength of the joint.
In order to eliminate stress concentration on the back side, the butt joint is eliminated and the shape is made into a scarf joint, and the direction of the outermost adhesive surface does not match the direction of stress, and the direction of the fibers and the adhesive direction match. It has been experimentally found that it is sufficient to form a finger shape in which the joint portion where the joining direction and the fiber direction of the veneer 6 are parallel is made as large as possible. However, it was extremely difficult to cut the front and back surfaces of a thin plywood board with a thickness of about 15 mm into a scarf joint shape that would fit accurately. In other words, the thickness of plywood varies from sheet to sheet or even within the same sheet, and according to the Japanese Agricultural Standards, thicknesses within the range of 3 to 20 mm are ±3% to ±4% of the indicated thickness.
Errors are recognized. Therefore, even if only the front and back surfaces of the plywood are cut into a scarf joint shape, the scarf joints on the front or back surfaces of the plywood will be at different levels or a gap will be created when they are fitted. Therefore, we further investigated ways to solve the above drawbacks and found that when joining plywood in a direction parallel to the fiber direction of the front veneer, we applied finger processing with a butt joint that does not cut the front veneer, and after fitting and By grinding the fitting portion smoothly into a scarf joint shape, we have completed a method for joining smooth plywood with high strength that can absorb variations in the thickness of the plywood. That is, in the present invention, the end portions of the front veneers 7 of the plywood boards 1 and 2 facing each other in parallel to the fiber direction are cut into a pair of fingers that fit into each other, and these are sequentially fitted and bonded to join the plywood boards. In the finger joint method of
Parts of the front and back surfaces of the plywood boards 1 and 2 at the fitting part are cut into a butt joint shape 9 that leaves the front veneer 7 and the back veneer 8, and then the plywood 1,
After fitting the pair of finger parts of 2 with a commonly used adhesive and curing the adhesive, the plywood 1 and 2
Front veneer 7 or front veneer 7 and back veneer 8 including the fitting part
This relates to a method for joining the ends of plywood, which is characterized by grinding smoothly to a thickness such that the butt joint shape 9 becomes a scarf joint shape. The present invention will be explained in detail with reference to the drawings. FIG. 3 is a perspective view showing finger-finished plywood joined by the method of the present invention. That is, 1 and 2 are plywood with a thickness of about 5 mm to 15 mm, and the fiber direction of the front veneer 7 and back veneer 8 of the plywood is parallel to the joining direction of the plywood, and the front veneer 7 and the back veneer 8 are The butt joint portion 9 of No. 8 is cut to such an extent that a portion of the front veneer 7 and the back veneer 8 remain. Regarding the pitch and length of the fingers, it is preferable that the ratio of the total length of the finger portions to the thickness of the plywood is 6 or more, and the finger pitch is 2 or more from the viewpoint of the bending strength of the plywood. Finger processing is done using a regular wood cutter. Then, the plywood is fitted as shown in FIG. A commonly used urea resin, phenol resin, urethane resin, epoxy resin, vinyl acetate resin adhesive, etc. is interposed in the fitting portion. The adhesive may be cured by leaving it at room temperature or by applying heat pressure. FIG. 5 is a perspective view showing the state in which the surfaces of the front veneer 7 and back veneer 8 including the fitting portion of the plywood obtained in the above steps have been ground smooth to a thickness such that the butt joint portion has a scarf joint shape. It is. Grinding of the front and back sides of the plywood is carried out using a grinding machine such as a regular sander or planer. Note that even if only the front veneer surface of the plywood is ground and a butt joint is left on the back veneer surface, sufficient bonding strength can be obtained for practical use. As described above, the bonded plywood manufactured by the method of the present invention is bonded because the front veneer or front veneer and back veneer of the plywood are joined in a scarf joint shape, and the core board part is joined in a finger joint shape. Even when a bending load perpendicular to the direction is applied, stress does not concentrate on the joints on the front and back surfaces, and the front and back veneers move against the bending load as compressive and tensile resistance. Despite being a finger joint, the desired strength can be obtained by taking advantage of the advantages of a scarf joint. The front and back veneers of the plywood are bonded in a butt joint shape in advance, and then ground smooth, so even if the plywood has uneven thickness, a bonded plywood with a smooth surface can be obtained, and even when pasted with thin decorative paper, etc. The bonded plywood obtained by the method of the present invention has an extremely wide range of uses as a substrate for decorative plywood, such as being able to produce long and wide decorative plywood with inconspicuous joints. Next, examples of the present invention will be described. Example 1 A 5-ply plywood board with a finished thickness of 8 mm, consisting of front and back veneers with a thickness of 1.0 mm, a middle plate with a thickness of 2.4 mm, and a core plate with a thickness of 1.35 mm, has two finger pitches shaped as shown in Figure 3.
The pitch width is 4mm, the finger length is 15mm, and the front
Finger joint processing with a depth of 0.2 mm was applied to the back veneer. Next, the fingers of the plywood were fitted with a urea resin adhesive as shown in FIG. 4, and then hot pressed at 110° C. for 2 minutes to harden the adhesive and join. Subsequently, the front and back surfaces of the bonded plywood were ground by a thickness of 0.3 mm from the front and back veneer surfaces using a thickness regulating sander to obtain a bonded board with a desired thickness of 7.4 mm as shown in FIG. As a comparative example, a 5-ply plywood consisting of a veneer structure with the same thickness as in Example 1 was processed with a finger joint in a conventional shape in which the front and back veneers were cut, although the dimensions were the same as in Example 1. After adhesive bonding, the surfaces of the front and back veneers are ground to determine the thickness in the same manner as in Example 1.
It was made of 7.4mm bonded plywood. The bonded plywood produced by the method of the present invention and the bonded plywood of the comparative example were subjected to a bending test. As shown in Table 1, the bending strength of the bonded plywood according to the method of the present invention was approximately 80% that of the raw plywood, while the bending strength of the bonded plywood of the comparative example was approximately 35% of that of the raw plywood. I could only obtain the strength of . [Table] [Bending strength (Kg/cm ² ) was determined by the following formula through a load test using three-point support. Bending strength = 3PbL/2bh ² (Kg/cm ² ) Pb: Maximum load (Kg) L: Span (cm) b: Width (cm) h: Thickness (cm)]

[Brief explanation of drawings]

FIG. 1 is a perspective view showing plywood joined by the conventional scarf joint method, and FIG. 2 is a perspective view showing wood joined by the conventional finger joint method. FIG. 3 is a perspective view showing a pair of fingered plywood used in the method of the present invention. FIG. 4 shows a state in which the finger portions of FIG. 3 are joined, and FIG. 5 is a perspective view showing a desired joined plywood in which the joined parts of the joined plywood shown in FIG. 4 are ground smooth. 1, 2...Thin plywood to be joined, 3, 4...Thick wood to be joined, 5...Butt joint processing part of thick wood, 6...Middle board of plywood, 7...Top veneer of plywood, 8 ... Back veneer of plywood, 9... Butt joint processing part of front veneer and back veneer of plywood.

Claims (1)

[Claims] 1. Ends of the front veneer 7 of the plywood boards 1 and 2 facing each other in parallel to the fiber direction are cut into a pair of fingers that fit into each other, and these are sequentially fitted and bonded. In the finger joint method for joining plywood, first, the shape of the pair of fingers applied to the ends of the plywood 1 and 2 is such that when the plywood 1 and 2 are fitted together, the shape of the plywood 1 and 2 at the fitting part is Parts of the front and back surfaces are cut into a butt joint shape 9 that leaves the front veneer 7 and back veneer 8, and then the plywood 1 and 2 are cut.
After fitting the pair of finger parts with a commonly used adhesive and curing the adhesive, the front veneer 7 or the front veneer 7 and the back veneer 8 including the fitted parts of the plywood 1 and 2 are assembled.
A method for joining the ends of plywood, characterized by grinding smoothly to a thickness such that the butt joint shape 9 becomes a scarf joint shape.